1. Field of the Invention
The present invention relates in general to an optical pickup device used in, for example, a compact disc player, for reading data recorded on an optical disc, and more particularly to an optical pickup device using holographic optical elements.
2. Description of the Background Art
Recently, the use of optical discs such as compact discs and laser discs have been greatly increased. In the future, these optical discs will be used in all technical fields, by virtue of their advantages, including the capability of storing a lot of information and convenience of use.
Such optical discs require an optical pickup device for reading information recorded thereon.
With reference to FIG. 1, a known optical pickup device comprises a laser diode 1 used as a light source, and a half mirror 2 reflecting the laser beam emitted from the laser diode 1. In order to read the information recorded on the optical disc 3, the laser beam reflected by the half mirror 2 is focused on the disc 3. To achieve the above object, a 45.degree. reflection mirror 4 and a focusing lens 5 are positioned between the half mirror 2 and the optical disc 3. Here, the 45.degree. reflection mirror 4 reflects the laser beam reflected by the half mirror 2 to the focusing lens 5 which focuses the laser beam on the disc 3. The known optical pickup device further includes a condensing lens 6 which condenses the laser beam, reflected by the optical disc 3, to a photo detector 7 which detects the condensed laser beam so as to read the information recorded on the disc 3.
In the above optical pickup device, the laser beam emitted from the laser diode 1 is reflected by the half mirror 2 and in turn focused on the optical disc 3 by way of the 45.degree. reflection mirror 4 and the focusing lens 5.
The laser beam focused on the optical disc 3 is, thereafter, reflected by the disc 3 and varied in its light intensity in accordance with different shapes of the recorded bumps or pits of the optical disc 3. The laser beam reflected by the disc 3 reversely passes through the above optical path. That is, the reflected laser beam is transmitted through the half mirror 2 and condensed by the condensing lens 6 to the photo detector 7 adapted for detecting a laser beam.
That is, the intensity of the laser beam condensed by the condensing lens 6 is detected by the photo detector 7, thereby achieving the reading of the information recorded on the optical disc 3.
However, the known optical pickup device undesirable has a large optical system since it should be provided with the half mirror 2 as well as the 45.degree. reflection mirror 4. Additionally, the laser diode 1 and the photo detector 7 are separately provided in the optical pickup device and this makes the size of the pickup device larger. In addition, a relatively longer time elapses from when the laser beam, reflected to and focused on the optical disc 3, reaches the photo detector 7, so that the known optical pickup device carries out the information reading operation slowly. Furthermore, all the elements of the known pickup device are separately mounted, thus requiring a longer assembling time, deteriorating the assemblage and resulting in increase of manufacturing cost.